Automotive fuel production from biomass on any meaningful scale is largely limited in practice to the fermentative processing of either starch hydrolysates or sucrose to ethanol. Although cellulosic ethanol and biodiesel are alternatives to agriculturally-derived ethanol, there are limitations associated with their use. A key issue in the case of cellulosic ethanol is the difficult and expensive derivation of fermentable sugars from lignocellulosic biomass. Beyond this, there are the limitations inherent in the fermentation process in terms of rate, efficiency, and the cost of isolating pure ethanol from a dilute aqueous solution. Additionally, ethanol is volatile, toxic, hydrophilic, potentially corrosive to engine components, and of relatively low energy content compared to gasoline or diesel fuel.
Furan-based biofuels, such as those produced from cellulose, are an alternative to ethanol as a biofuel. Cellulose has been used to produce ethanol, but can also be used to prepare furanic biofuels by way of 5-(chloromethyl)furfural (CMF). CMF can be converted into 5-(ethoxymethyl)furfural (EMF) by mixing with ethanol. EMF is already being commercially developed as a promising diesel fuel additive. Alternatively, hydrogenolysis of the halogen in CMF gives 5-methylfurfural (MF), an attractive biofuel candidate, since only 2 g of H2 are required for the synthesis of 110 g of MF, as opposed to 46 g of ethanol in the synthesis of 154 g of EMF.
CMF was described as early as 1901 as a product from the action of dry hydrogen chloride on cellulose. While the conversion for this reaction was low (12%), a related study in which anhydrous HBr was employed showed that the bromo analogue of CMF could be produced from cellulose in up to 48% yield, although glucose itself underwent the reaction in only 11% yield. A number of additional reports address the preparation of CMF from fructose, which is consistent with the related, facile conversion of fructose into 5-(hydroxymethyl)furfural (HMF). Fructose is expensive and is not considered a viable feedstock for biofuel or value added product synthesis.
Substituted furans and their derivatives, such as HMF, furfural, and levulinic acid, are also important value-added products, and are used as feedstocks for the production of resins, polymers, and chemical intermediates of use to commodity industries, such as the healthcare, cosmetic, materials, and foodstuff industries.
Other furan products, such as furfural, can be prepared from hemicellulose. Hemicellulose is the second most abundant organic material in nature, representing 25-35% of lignocellulose by mass (J. Ind. Microbiol. Biotechnol. 2003, 30, 279). In mainstream ethanol production, hemicellulose goes unutilized, since conventional yeasts cannot ferment C5 sugars. Although work both with native and recombinant microorganisms has led to strains that can utilize xylose (the most abundant pentose in hemicellulose), limitations in rate, yield, stability, and inhibitor tolerance have presented obstacles to industrial applications of this technology (Adv. Biochem. Engin. Biotechnol. 2007, 108, 179; Adv. Biochem. Engin. Biotechnol. 2007, 108, 147; Biotech Adv. 2007, 25, 425; Appl. Microbiol. Biotechnol. 2007, 74, 937).
What is needed is a process for preparing CMF, furfural, and associated furanic products, in high yields from biomass such as cellulose and hemicellulose containing materials. Surprisingly, the present invention meets this and other needs.